Quantum dots and devices including the same

ABSTRACT

A quantum dot includes a core-shell structure including a core including a first semiconductor nanocrystal and a shell disposed on the core, and including a material at least two different halogens, and the quantum dot does not include cadmium.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2015-0184033 filed in the Korean IntellectualProperty Office on Dec. 22, 2015, and all the benefits accruingtherefrom under 35 U.S.C. § 119, the entire content of which isincorporated herein in its entirety by reference.

BACKGROUND

1. Field

Quantum dots and devices including the same are disclosed.

2. Description of the Related Art

Nanoparticles have physical characteristics (e.g., energy bandgaps andmelting points) that depend on particle size, unlike bulk materials. Forexample, a semiconductor nanocrystal, also known as a quantum dot (QD)is a semiconductor material having a crystalline structure with a sizeof several nanometers. Quantum dots have such a small size that theyhave a large surface area per unit volume and exhibit quantumconfinement effects, and thus have different physicochemicalcharacteristics from the characteristics of the bulk material. Quantumdots may absorb light from an excitation source and may emit lightenergy corresponding to an energy bandgap of the quantum dot. In thequantum dots, the energy bandgap may be selected by controlling thesizes and/or the compositions of the nanocrystals. Also, QDs havedesirable photoluminescence properties and have a high color purity.Therefore, QD technology is used for various applications, including adisplay device, an energy device, a bio-light emitting element, or thelike.

A quantum dot having a core-shell structure may have a slightlyincreased luminous efficiency due to surface passivation by the shell,however most of these systems include cadmium. Cadmium poses seriousenvironmental problems, and thus it is desirable to provide acadmium-free semiconductor nanocrystal particle with desirable lightemitting properties.

Electronic devices including quantum dots may be operated in a hightemperature environment; and thereby luminous efficiency of the quantumdots may be adversely affected by the ambient temperature. Therefore,there is a need to develop quantum dots in which the negative impact oftemperature is reduced.

SUMMARY

An embodiment provides environmentally-friendly quantum dots havingimproved photoluminescence properties and temperature characteristics.

Another embodiment provides a method of producing the quantum dots.

Yet another embodiment provides a polymer composite including thequantum dots.

Still another embodiment provides an electronic device including thequantum dots.

In an embodiment, a quantum dot includes a core-shell structureincluding a core including a first semiconductor nanocrystal; and ashell disposed on the core, the shell including a crystalline oramorphous material and at least two different halogens, wherein thequantum dot does not include cadmium.

In case of the quantum dot, a solid state photoluminescence quantumefficiency of the quantum dot when measured at 90° C. or greater isgreater than or equal to about 95% of a solid state photoluminescencequantum efficiency of the quantum dot when measured at 25° C.

The at least two halogens may include fluorine; and at least one of theother halogens include chlorine, bromine, iodine, or a combinationthereof.

The quantum dot may have a solid state photoluminescence quantumefficiency, when measured at a temperature of 100° C., that is greaterthan or equal to about 95% of the solid state photoluminescence quantumefficiency thereof when measured at a temperature of 25° C.

The quantum dot may have a solid state photoluminescence quantumefficiency, when measured at a temperature of 150° C., that is greaterthan or equal to about 80% of the solid state photoluminescence quantumefficiency thereof measured at a temperature of 25° C.

The halogen may present in or on the shell as a metal halide or can bedoped therein.

The shell may have a thickness of at least one monolayer of thecrystalline or amorphous material, and at least one of the halogens maybe present at or outside (i.e., after) the thickness of the onemonolayer.

A total amount of the halogens may be greater than or equal to about 30atomic percent, with respect to a total amount of a metal included inthe core.

The first semiconductor nanocrystal may include a first metal includinga Group II metal excluding cadmium, a Group III metal, a Group IV metal,or a combination thereof.

The material of the shell may include at least one second metal that isdifferent from the first metal and includes a Group I metal, a Group IImetal excluding cadmium, a Group III metal, a Group IV metal, or acombination thereof.

The first semiconductor nanocrystal may include a Group II-VI compoundexcluding a cadmium-containing compound, a Group III-V compound, a GroupIV-VI compound, a Group IV element or compound, a Group compound, aGroup I-II-IV-VI compound, or a combination thereof.

The crystalline or amorphous material of the shell may include a GroupII-VI compound excluding a cadmium-containing compound, a Group III-Vcompound, a Group IV-VI compound, a Group IV element or compound, aGroup compound, a Group I-II-IV-VI compound, a metal-containing halogencompound (e.g., a metal halide), a metal oxide, or a combinationthereof.

The Group II-VI compound may include ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe,HgTe, MgSe, MgS, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, HgZnS,HgZnSe, HgZnTe, MgZnSe, MgZnS, HgZnTeS, HgZnSeS, HgZnSeTe, HgZnSTe, or acombination thereof,

the Group III-V compound may include GaN, GaP, GaAs, GaSb, AlN, AlP,AlAs, AlSb, InN, InP, InAs, InSb, GaNP, GaNAs, GaNSb, GaPAs, GaPSb,AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb,GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb,GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, or acombination thereof,

the Group IV-VI compound may include SnS, SnSe, SnTe, PbS, PbSe, PbTe,SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe,SnPbSSe, SnPbSeTe, SnPbSTe, or a combination thereof,

the Group I-III-VI compound may include CuInSe₂, CuInS₂, CuInGaSe,CuInGaS, or a combination thereof,

the Group II-III-VI compound may include ZnGaS, ZnAlS, ZnInS, ZnGaSe,ZnAlSe, ZnInSe, ZnGaTe, ZnAlTe, ZnInTe, ZnGaO, ZnAlO, ZnInO, HgGaS,HgAlS, HgInS, HgGaSe, HgAlSe, HgInSe, HgGaTe, HgAlTe, HgInTe, MgGaS,MgAlS, MgInS, MgGaSe, MgAlSe, MgInSe, or a combination thereof,

the Group I-II-IV-VI compound may include CuZnSnSe, CuZnSnS, or acombination thereof,

the Group IV element or compound may include Si, Ge, SiC, SiGe, or acombination thereof,

the metal-containing halogen compound may be LiF, NaF, KF, BeF₂, MgF₂,CaF₂, SrF₂, CuF, AgF, AuF, ZnF₂, HgF₂, AlF₃, GaF₃, InF₃, SnF₂, PbF₂,LiCl, NaCl, KCl, BeCl₂, MgCl₂, CaCl₂, SrCl₂, CuCl, AgCl, AuCl, ZnCl₂,HgCl₂, AlCl₃, GaCl₃, InCl₃, SnCl₂, PbCl₂, LiBr, NaBr, KBr, BeBr₂, MgBr₂,CaBr₂, SrBr₂, CuBr, AgBr, AuBr, ZnBr₂, HgBr₂, AlBr₃, GaBr₃, InBr₃,SnBr₂, PbBr₂, LiI, NaI, KI, BeI₂, MgI₂, CaI₂, SrI₂, CuI, AgI, AuI, ZnI₂,HgI₂, AlI₃, GaI₃, InI₃, SnI₂, PbI₂, or a combination thereof, and

the metal oxide may include In₂O₃, PbO, HgO, MgO, Ga₂O₃, Al₂O₃, ZnO,SiO₂, zinc oxysulfide, zinc oxyselenide, zinc oxysulfide selenide,indiumphosphide oxide, indiumphosphide oxysulfide, or a combinationthereof.

The first semiconductor nanocrystal may include a Group III-V compoundand the shell may include a Group II-VI compound.

The quantum dot may have a quantum yield of greater than or equal toabout 85%.

Another embodiment provides a method of producing a quantum dot, themethod including:

obtaining a first mixture including a first precursor, a ligandcompound, and a solvent;

adding a second precursor, a first halogen source, and a firstsemiconductor nanocrystal to the first mixture to obtain a secondmixture;

heating the second mixture to a reaction temperature effective toperform a reaction between the first precursor and the second precursor;and

adding a second halogen source to the second mixture after initiatingthe reaction between the first precursor and the second precursor,

wherein a core-shell structure of the quantum dot includes a coreincluding a first semiconductor nanocrystal, and a shell including acrystalline or amorphous material disposed on the core, wherein thequantum dot does not include cadmium, and wherein the shell includes atleast two halogens.

In an embodiment, the at least two halogens includes fluorine; and atleast one of the other halogens is chlorine, bromine, iodine, or acombination thereof.

The quantum dot may have a solid state photoluminescence quantumefficiency at a temperature of about 90° C. or higher that is greaterthan or equal to about 95% of the solid state photoluminescence quantumefficiency thereof as measured at 25° C.

The first precursor may include at least one second metal that isselected from a Group II metal excluding cadmium, a Group III metal, aGroup IV metal, or a combination thereof, and the first precursor may bein a form of a metal powder, an alkylated metal compound, a metalalkoxide, a metal carboxylate, a metal nitrate, a metal perchlorate, ametal sulfate, a metal acetylacetonate, a metal halide, a metal cyanide,a metal hydroxide, a metal oxide, or a metal peroxide.

The second precursor may include a Group V element, a Group IV element,or a compound including the Group V element, or the Group IV element.

The ligand compound may include a compound of the formula RCOOH, RNH₂,R₂NH, R₃N, RSH, R₃PO, R₃P, ROH, RCOOR′, RPO(OH)₂, R₂POOH (wherein, eachR and R′ are independently a substituted or unsubstituted C1 to C24aliphatic hydrocarbon group or a substituted or unsubstituted C6 to C20aromatic hydrocarbon group), or a combination thereof.

The first halogen source may include fluorine.

The second halogen source may include chlorine, bromine, iodine, or acombination thereof.

The first halogen source may include HF, NH₄F, LiF, NaF, KF, BeF₂, MgF₂,CaF₂, SrF₂, CuF, AgF, AuF, ZnF₂, HgF₂, AlF₃, GaF₃, InF₃, SnF₂, PbF₂,HBF₄, a fluorine-containing ionic liquid, or combination thereof.

The second halogen source may include HCl, NH₄Cl, HBr, NH₄Br, LiCl,NaCl, KCl, BeCl₂, MgCl₂, CaCl₂, SrCl₂, CuCl, AgCl, AuCl, ZnCl₂, HgCl₂,AlCl₃, GaCl₃, InCl₃, SnCl₂, PbCl₂, LiBr, NaBr, KBr, BeBr₂, MgBr₂, CaBr₂,SrBr₂, CuBr, AgBr, AuBr, ZnBr₂, HgBr₂, AlBr₃, GaBr₃, InBr₃, SnBr₂,PbBr₂, LiI, NaI, KI, BeI₂, MgI₂, CaI₂, SrI₂, CuI, AgI, AuI, ZnI₂, HgI₂,AlI₃, GaI₃, InI₃, SnI₂, PbI₂, an aliphatic hydrocarbon chloride, analiphatic hydrocarbon bromide, an aliphatic hydrocarbon iodide, or acombination thereof.

The method may further include adding the second precursor after theinitiation of a reaction between the first precursor and the secondprecursor.

In the method, the second halogen source may be used in a greater amountthan the first halogen source.

In another embodiment, a quantum dot polymer composite includes apolymer matrix; and the aforementioned quantum dot dispersed in thepolymer matrix.

The polymer matrix may include a thiolene polymer, a (meth)acrylatepolymer, a urethane polymer, an epoxy polymer, a vinyl polymer, asilicone polymer, or a combination thereof.

Another embodiment provides an electronic device including theaforementioned quantum dot.

According to an embodiment, environmentally friendly quantum dots thatmay mitigate the thermal quenching phenomenon and have improved solidstate quantum efficiency may be provided.

The quantum dots of the embodiments may find their use in many fieldssuch as various display devices, biological labeling (e.g., a biosensor,a bio-imaging, and the like), a photo-detector, a hybrid composite, andthe like.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic illustration of a cross-section of an embodimentof a quantum dot;

FIG. 2 is a graph of quantum efficiency (QE, %) versus temperature (°C.) showing the results of Experimental Example 2-1, showing the thermalquenching related properties of quantum dot-polymer composite sheetsprepared in Experimental Example 1-1; and

FIG. 3 is an exploded view showing an electronic device (e.g. a liquidcrystal display, LCD) including the quantum dot according to anon-limiting embodiment.

DETAILED DESCRIPTION

Advantages and characteristics of this disclosure, and a method forachieving the same, will become evident referring to the followingexemplary embodiments together with the drawings attached hereto. Theembodiments, may, however, be embodied in many different forms andshould not be construed as being limited to the embodiments set forthherein. If not defined otherwise, all terms (including technical andscientific terms) in the specification may be defined as commonlyunderstood by one skilled in the art. The terms defined in agenerally-used dictionary may not be interpreted ideally orexaggeratedly unless clearly defined. In addition, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising,” will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.

Further, the singular includes the plural unless mentioned otherwise.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification.

It will be understood that when an element such as a layer, film,region, or substrate is referred to as being “on” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present.

It will be understood that, although the terms “first,” “second,”“third,” etc. may be used herein to describe various elements,components, regions, layers, and/or sections, these elements,components, regions, layers, and/or sections should not be limited bythese terms. These terms are only used to distinguish one element,component, region, layer, or section from another element, component,region, layer, or section. Thus, “a first element,” “component,”“region,” “layer,” or “section” discussed below could be termed a secondelement, component, region, layer, or section without departing from theteachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “At least one” is not to be construed as limiting “a” or“an.” It will be further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±10%, or 5% of the stated value.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

As used herein, when a definition is not otherwise provided, the term“substituted” refers to a group or compound wherein at least one of thehydrogen atoms thereof is substituted with a C1 to C30 alkyl group, a C2to C30 alkenyl group, a C2 to C30 alkynyl group, a C6 to C30 aryl group,a C7 to C30 alkylaryl group, a C1 to C30 alkoxy group, a C1 to C30heteroalkyl group, a C3 to C30 heteroalkylaryl group, a C3 to C30cycloalkyl group, a C3 to C15 cycloalkenyl group, a C3 to C30cycloalkynyl group, a C2 to C30 heterocycloalkyl group, a halogen (—F,—Cl, —Br, or —I), a hydroxy group (—OH), a nitro group (—NO₂), a cyanogroup (—ON), an amino group (—NRR′ wherein R and R′ are independentlyhydrogen or a C1 to C6 alkyl group), an azido group (—N₃), an amidinogroup (—C(═NH)NH₂), a hydrazino group (—NHNH₂), a hydrazono group(═N(NH₂)), an aldehyde group (—C(═O)H), a carbamoyl group (—C(O)NH₂), athiol group (—SH), an ester group (—C(═O)OR, wherein R is a C1 to C6alkyl group or a C6 to C12 aryl group), a carboxyl group (—COOH) or asalt thereof (—C(═O)OM, wherein M is an organic or inorganic cation), asulfonic acid group (—SO₃H) or a salt thereof (—SO₃M, wherein M is anorganic or inorganic cation), a phosphoric acid group (—PO₃H₂) or a saltthereof (—PO₃MH or —PO₃M₂, wherein M is an organic or inorganic cation),and a combination thereof.

As used herein, the term “hydrocarbon group” refers to a monovalentgroup containing carbon and hydrogen (e.g., alkyl group, alkenyl group,alkynyl group, or aryl group) formed by a removal of a hydrogen atomfrom an aliphatic or aromatic hydrocarbon such as alkane, alkene,alkyne, or arene. In the hydrocarbon group, at least one methylene(—CH₂—) moiety may be replaced with an oxide (—O—) moiety.

As used herein, the term “metal” includes a metal and a semi-metal.

As used herein, the term “alkyl” refers to a linear or branched,saturated monovalent hydrocarbon group (e.g., methyl, hexyl, etc.).

As used herein, the term “alkenyl” refers to a linear or branchedmonovalent hydrocarbon group having at least one carbon-carbon doublebond.

As used herein, the term “aryl” refers to a monovalent group formed byremoving one hydrogen atom from at least one aromatic ring (e.g., phenylor naphthyl).

As used herein, when a definition is not otherwise provided, the term“hetero” refers to inclusion of 1 to 3 heteroatoms that can be N, O, S,Si, P, or a combination thereof.

As used herein, the term “alkylene group” refers to a straight orbranched saturated aliphatic hydrocarbon group having a valence of atleast two, optionally substituted with one or more substituents. Theterm “arylene group” refers to a functional group having a valence of atleast two obtained by removal of at least two hydrogens in an aromaticring, optionally substituted with one or more substituents.

Further as used herein, when a definition is not otherwise provided, analkyl group is a C1 to C20 alkyl, or a C1 to C12 alkyl, or a C1 to C6alkyl.

As used herein, the term “Group” refers to a Group of Periodic Table.

As used herein, “Group I” refers to Group IA and Group IB, and examplesof Group I include Li, Na, K, Ru, and Cs, but are not limited thereto.

As used herein, “Group II” refers to Group IIA and Group IIB, andexamples of Group II include Cd, Zn, Hg, and Mg, but are not limitedthereto, except where Cd is specifically excluded.

As used herein, “Group III” refers to Group IIIA and Group IIIB, andexamples of Group III include Al, In, Ga, and TI, but are not limitedthereto.

As used herein, “Group IV” refers to Group IVA and Group IVB, andexamples of a Group IV include Si, Ge, and Sn, but are not limitedthereto.

As used herein, the term “metal” may include a semi-metal such as Si.

As used herein, the term “doping” refers to the inclusion of a dopant ina crystal structure. In an exemplary embodiment, inclusion of a dopantin the crystal structure does not substantially change the crystalstructure. For example, a dopant atom (e.g., a halogen) may be asubstituted for an atom in a crystal structure, or present in theinterstices of a crystal lattice. In some embodiments, the X-raydiffraction spectrum of a doped compound is substantially the same asthe X-ray diffraction spectrum of an undoped compound. In an embodiment,the presence of the dopant in the crystal structure may be confirmed,for example, by X-ray photoelectron spectroscopy, energy dispersive Xray spectroscopy, or inductively coupled plasma-atomic emissionspectroscopy (ICP-AES).

As used herein, the term quantum yield” (QY) is a value determined froma photoluminescence spectrum obtained by dispersing quantum dots intoluene, and is calculated with respect to the photoluminescent peak ofan ethanol solution of coumarin dye (absorption (optical density) at 458nanometers (nm) is 0.1).

As used herein, “solid state photoluminescence quantum efficiency (QE)”is a value obtained from a photoluminescence intensity of quantum dotsdispersed in a solid matrix. A ratio of the solid statephotoluminescence QE at a predetermined temperature to the solid statephotoluminescence QE at a reference temperature (e.g., 25° C.) mayreflect the properties of the quantum dot regarding “thermal quenchingphenomenon.” For example, a photoluminescence intensity of a quantumdot-solid matrix film including a polymer matrix and a plurality ofquantum dots dispseresd therein is first measured at room temperature(e.g., 25° C.), and a photoluminescence intensity of the quantumdot-solid matrix film is subsequently measured at increasingtemperatures. The ratio of photoluminescence intensity at eachtemperature with respect to the photoluminescence intensity at 25° C. isthe relative photoluminescence intensity (%), which may serve as anindicator of the quantum dot's property as to the thermal quenching.

A quantum dot according to an embodiment has a core-shell structure thatincludes a core including a first semiconductor nanocrystal and a shellincluding a crystalline or amorphous material disposed on the coresurface (e.g., on at least a portion of a surface or on the entiresurface of the core). The shell may include a multi-layered shellincluding at least two layers. When the shell is a multi-layered shell,each layer (e.g., each of the adjacent layers) may have the same or adifferent composition. Without wishing to be bound by any theory, in theaforementioned quantum dot, the shell may effectively passivate asurface of the core (e.g., the traps thereon) to increase the luminousefficiency and to enhance the stability of the quantum dot. In addition,the shell may serve as a physical barrier that improves the stability ofa core that may be otherwise susceptible to degradation by exposure tothe ambient environment. The material of the shell may be crystalline oramorphous.

The quantum dot does not include cadmium, and the shell of the quantumdot includes at least one halogen (for example, fluorine, chlorine,bromine, iodine, or a combination thereof). In an embodiment, the shellof the quantum dot may include at least two halogens, and the halogensmay include a fluorine (as a first halogen); and chlorine, bromine,iodine, or a combination thereof. The halogen may be doped or in a formof a metal halide in the shell.

The solid state photoluminescence quantum efficiency of the quantum dot,when measured at a temperature of 90° C. or greater, may be greater thanor equal to about 95% of the solid state photoluminescence quantumefficiency of the quantum dot when measured at a temperature of 25° C.

The “solid state photoluminescence quantum efficiency” is related to aphotoluminescence intensity measured for the quantum dots dispersed in asolid matrix (instead of a solution). The photoluminescence intensitymay be measured by a spectrometer at a predetermined wavelength ofexcitation light.

Nanocrystal particles including a semiconductor material (i.e., quantumdots) may have an energy bandgap that varies based on size andcomposition, and may have desirable photoluminescence properties. Thus,these compounds may be suitable as a material applicable for variousfields such as a display, an energy device, a semiconductor, and a biodevice.

Quantum dots have been included in various electronic devices, and theoperating temperature of the devices may increase up to a temperaturefar higher than room temperature. Accordingly, the quantum dots may besubjected to a high temperature environment when they are used in theactual devices. For example, the quantum dots may be exposed to atemperature that is greater than about 70° C., greater than or equal toabout 90° C., greater than or equal to about 100° C., greater than orequal to about 110° C., greater than or equal to about 120° C., greaterthan or equal to about 130° C., or greater than or equal to about 150°C. For example, in the case of a high power LED, the quantum dots tendto be exposed to a relatively high temperature due to the thermalemission generated from the p-n junction and the light conversion layerand the heat generated from the quantum dots themselves, which may beunfavorable for the application of quantum dots. While not wanting to bebound by theory, it is understood that this is because thephotoluminescence properties of the quantum dots may be affected by thetemperature. For example, thermal quenching may decrease the luminousefficiency of quantum dots at a high temperature.

Many hypotheses have been suggested regarding the cause of the thermalquenching phenomenon of the quantum dots. The quantum dots (QD) have ahigh ratio of a surface area with respect to a volume, and thus may havea great number of the surface related trap states. The trap states maybecome a path that moves the excited charge carriers into thephotoluminescence quenching center. In other words, the trap states onthe QD surface may trap the charge carriers, causing a decrease in thephotoluminescence (PL). As the temperature increases, the number of thetrap states may be temporarily increased (for example, due to thegeneration of the thermally-activated trap states), and the thermallyactivated carrier may be easily excited at such a trap state, activatingthe trapping and thereby causing a decrease in the PL intensity. Inaddition, rather than dropping to the ground state with light emission,the carriers trapped in the trap state are escaping and thermallyscattering (for example, via the non-radiative process), and this maylead to the decrease of their PL intensity.

Also, most of the quantum dots capable of exhibiting good performance interms of the photoluminescence properties and stability include cadmium(Cd). For example, the quantum dots including Cd in the core and/or theshell may show a relatively high luminous efficiency, and the thermalquenching phenomenon is not significant for these quantum dots. However,as cadmium is one of the atoms posing serious environmental problems,the cadmium-free quantum dots have advantages in terms of theenvironment. A Group III-V compound semiconductor nanocrystal is acadmium free quantum dot, but it is not easy to control its synthesisreaction because the precursors used therein are very susceptible tooxidation and their activity is poor in comparison with thecadmium-based semiconductor nanocrystal (e.g., the CdSe-based quantumdot). As a type of the Group III-V semiconductor nanocrystal, thequantum dot including a Group III-V core such as InP have beenresearched intensively. Despite this fact, however, synthesis of theInP-based semiconductor is difficult and it may have photoluminescenceproperties and thermal stability that are inferior to those of theCd-based quantum dots.

The quantum dots according to an embodiment may achieve an improvementin thermal quenching phenomenon together with the increased luminousefficiency, even when they do not include cadmium.

The shell has a thickness of greater than or equal to 1 monolayer ofcrystalline or amorphous material (e.g., a thickness of 2 monolayers, 3monolayers, 4 monolayers, or higher), and the halogen or the secondhalogen may be present on or after the first monolayer or on or afterthe total number of monolayers. For example, the shell may have athickness of greater than or equal to about 0.3 nanometers (nm), forexample, a thickness of greater than or equal to about 0.6 nm, and thesecond halogen may be present outside a shell thickness of, for example,greater than or equal to 0.3 nm. In an embodiments, the shell has athickness of greater than or equal to 1 monolayer of the crystalline orthe amorphous material (e.g., 0.3 nm or more), and may include chlorine,bromine, iodine, or a combination thereof after the first monolayer. Inthe shell, the fluorine may be present at the interface between the coreand the shell or inside of the shell, but it is not limited thereto.

A total amount of the halogen may be greater than or equal to about 30atomic percent (at. %), for example greater than or equal to about 40at. %, greater than or equal to about 50 at. %, greater than or equal toabout 60 at. %, or greater than or equal to about 65 at. %, e.g., about30 at. % to about 90 at. %, about 30 at. % to about 80 at. %, or about30 at. % to about 70 at. %, with respect to a total amount of the metalincluded in the core. In an embodiment, the amount of fluorine includedin the quantum dots may be within a range of greater than 0 mole percent(mol %), (e.g., greater than or equal to about 0.1 mol %) to less thanor equal to about 20 mol % based on the total amounts of all atomsincluded in the quantum dot. According to an embodiment, the amount ofthe second halogen (i.e., chlorine, bromine, iodine, or a combinationthereof) included in the quantum dot may be within a range of greaterthan about 0 mol % (e.g., greater than or equal to about 0.1 mol %) andless than or equal to about 20 mol % based on a total amount of all theatoms included in the quantum dot.

Without wishing to be bound by any theory, it is estimated that theshell including the halogen (e.g., the first and second halogens) mayeffectively passivate the core and may reduce the number of trap statesthat may cause the thermal quenching phenomenon in the quantum dotsaccording to an embodiment.

Accordingly, the quantum dots of the embodiments may achieve theimprovement relating to the thermal quenching phenomenon and have theimproved luminous efficiency when they have a relatively thin shell.

Accordingly, the quantum dots according to an embodiment may show asolid state quantum efficiency measured at a temperature of 100° C. thatis greater than or equal to about 95%, for example, greater than orequal to about 96%, or greater than or equal to about 97% of their solidstate quantum efficiency measured at a temperature of 25° C. Inaddition, in an embodiment, a solid state quantum efficiency at 150° C.of the quantum dots may be greater than or equal to about 80%, forexample, greater than or equal to about 81%, or greater than or equal toabout 82% of a solid state quantum efficiency at 25° C. Thus the quantumdots of an embodiment may be used in various optical devices operated ata relatively high temperature (e.g., an LED, various light emittingdevices, quantum dot lasers, etc.) and are environmentally friendlybecause they do not include cadmium.

In the quantum dots according to an embodiment, the first semiconductornanocrystal of the core may include a metal comprising a Group II metalexcluding cadmium, a Group III metal, a Group IV metal, or a combinationthereof.

The material of the shell, which may be crystalline or amorphous, mayhave the same or different composition as the first nanocrystal. Thecrystalline or amorphous material may include a Group II-VI compound, aGroup III-V compound, a Group IV-VI compound, a Group IV compound, ametal fluoride, a metal oxide, or a combination thereof. The shell maybe crystalline or amorphous. The semiconductor material of the shell mayhave a larger bandgap than the band gap of the core material (i.e., thefirst nanocrystal).

The first semiconductor nanocrystal may include a Group II-VI compoundexcluding a cadmium-containing compound, a Group III-V compound, a GroupIV-VI compound, a Group IV compound, a Group compound, a GroupI-II-IV-VI compound, or a combination thereof.

The crystalline or amorphous material of the shell may include a GroupII-VI compound excluding a cadmium-containing compound, a Group III-Vcompound, a Group IV-VI compound, a Group IV compound, a Group compound,a Group I-II-IV-VI compound, a metal-containing halogen compound, ametal oxide, or a combination thereof.

The Group II-VI compound may comprise a binary element compoundcomprising ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, or acombination thereof; a ternary element compound comprising ZnSeS,ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, HgZnS, HgZnSe, HgZnTe, MgZnSe,MgZnS, or a combination thereof; and a quaternary element compoundcomprising HgZnTeS, HgZnSeS, HgZnSeTe, HgZnSTe, or combination thereof,

the Group III-V compound may comprise a binary element compoundcomprising GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs,InSb, or a combination thereof; a ternary element compound comprisingGaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb,InNP, InNAs, InNSb, InPAs, InPSb, or a combination thereof; and aquaternary element compound comprising GaAlNP, GaAlNAs, GaAlNSb,GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP,InAlNAs, InAlNSb, InAlPAs, InAlPSb, or a combination thereof,

the Group IV-VI compound may comprise a binary element compoundcomprising SnS, SnSe, SnTe, PbS, PbSe, PbTe, or a combination thereof; aternary element compound comprising SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe,PbSTe, SnPbS, SnPbSe, SnPbTe, or a combination thereof; and a quaternaryelement compound comprising SnPbSSe, SnPbSeTe, SnPbSTe, or a combinationthereof,

the Group compound may comprise CuInSe₂, CuInS₂, CuInGaSe, and CuInGaS,

the Group II-III-VI compound may comprise ZnGaS, ZnAlS, ZnInS, ZnGaSe,ZnAlSe, ZnInSe, ZnGaTe, ZnAlTe, ZnInTe, ZnGaO, ZnAlO, ZnInO, HgGaS,HgAlS, HgInS, HgGaSe, HgAlSe, HgInSe, HgGaTe, HgAlTe, HgInTe, MgGaS,MgAlS, MgInS, MgGaSe, MgAlSe, MgInSe, or a combination thereof,

the Group I-II-IV-VI compound may comprise CuZnSnSe, CuZnSnS, or acombination thereof,

the Group IV compound may comprise a single-element that may be Si, Ge,or a combination thereof; and a binary element compound comprising SiC,SiGe, or a combination thereof,

the metal-containing halogen compound may comprise LiF, NaF, KF, BeF₂,MgF₂, CaF₂, SrF₂, CuF, AgF, AuF, ZnF₂, HgF₂, AlF₃, GaF₃, InF₃, SnF₂,PbF₂, LiCl, NaCl, KCl, BeCl₂, MgCl₂, CaCl₂, SrCl₂, CuCl, AgCl, AuCl,ZnCl₂, HgCl₂, AlCl₃, GaCl₃, InCl₃, SnCl₂, PbCl₂, LiBr, NaBr, KBr, BeBr₂,MgBr₂, CaBr₂, SrBr₂, CuBr, AgBr, AuBr, ZnBr₂, HgBr₂, AlBr₃, GaBr₃,InBr₃, SnBr₂, PbBr₂, LiI, NaI, KI, BeI₂, MgI₂, CaI₂, SrI₂, CuI, AgI,AuI, ZnI₂, HgI₂, AlI₃, GaI₃, InI₃, SnI₂, PbI₂, or a combination thereof,and

the metal oxide may comprise In₂O₃, PbO, HgO, MgO, Ga₂O₃, Al₂O₃, ZnO,SiO₂, zinc oxysulfide, zinc oxyselenide, zinc oxysulfide selenide,indium phosphide oxide, indium phosphide oxysulfide, or a combinationthereof.

The core may include a Group III-V compound (e.g., InP) and the shellmay include a Group II-VI compound. The core may include indium and theshell may include at least three elements (ternary element compound orquaternary element compound). The core may further include Zn. Forexample, the core may be a Group III-V compound including Zn (e.g.,InPZn or InP(Zn)). Herein, the term InP(Zn) indicates the case where theZn is included in a surface thereof.

In an embodiment, the quantum dot may have a quantum yield (QY) ofgreater than or equal to about 85%. The quantum dot may have a fullwidth at half maximum (FWHM) of less than or equal to about 50 nm, forexample, less than or equal to about 45 nm, or less than or equal toabout 40 nm.

The quantum dot may absorb light in a wavelength of about 300 nm toabout 700 nm and may emit light in a wavelength of about 400 nm to about600 nm, about 600 nm to about 700 nm, or about 550 nm to about 650 nm,without limitations. The photoluminescence wavelengths may be controlledaccording to the compositions or the size of the quantum dot(core/shell).

The quantum dot may have a particle size (a diameter or a largest lengthof a straight line crossing a non-spherical particle) of about 1 nm toabout 100 nm, for example about 1 nm to about 20 nm, or about 1 nm toabout 10 nm or about 1 nm to about 5 nm. The shape of the quantum dot isnot particularly limited. For example, the quantum dot may have aspherical, pyramidal, multi-armed (or multipod), or a cubic shape, butit is not limited thereto.

The presence of a halogen in the quantum dot may be confirmed by anX-ray photoelectron spectroscopy (XPS), without limitation. In thequantum dot, the halogen may be present as being doped. The halogen mayreplace an atom in the crystal structure of the quantum dot or may bepresent as an interstitial atom. The halogen may be present in a form ofa halide of the metal included in the shell.

The quantum dot may include a coordinated organic ligand on its surface.The organic ligand may include any suitable ligand compounds and is notparticularly limited. For example, the ligand compound may include acompound of the formula RCOOH, RNH₂, R₂NH, R₃N, RSH, RH₂PO, R₂HPO, R₃PO,RH₂P, R₂HP, R₃P, ROH, RCOOR′, RPO(OH)₂, R₂POOH, wherein, R and R′ areeach independently a substituted or unsubstituted C1 to C24 alkyl group,a substituted or unsubstituted C2 to C24 alkenyl group, a substituted orunsubstituted C2 to C24 alkynyl group, or a substituted or unsubstitutedC6 to C20 aryl group, or a combination thereof. The organic ligandcompound is coordinated on the surface of the produced nanocrystal, andmay improve nanocrystal dispersion in a solution, which may enhance thephotoluminescence and electric characteristics. Specific examples of theorganic ligand compound may include thiol compounds such as methanethiol, ethane thiol, propane thiol, butane thiol, pentane thiol, hexanethiol, octane thiol, dodecane thiol, hexadecane thiol, octadecane thiol,or benzyl thiol; amines such as methane amine, ethane amine, propaneamine, butane amine, pentyl amine, hexyl amine, octyl amine, nonylamine,decylamine, dodecyl amine, hexadecyl amine, octadecyl amine, dimethylamine, diethyl amine, or dipropyl amine; carboxylic acid compounds suchas methanoic acid, ethanoic acid, propanoic acid, butanoic acid,pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, dodecanoicacid, hexadecanoic acid, octadecanoic acid, oleic acid, or benzoic acid;phosphines such as substituted or unsubstituted methyl phosphine (e.g.,trimethyl phosphine, methyldiphenyl phosphine, etc.), a substituted orunsubstituted ethyl phosphine (e.g., triethyl phosphine, ethyldiphenylphosphine, etc.), a substituted or unsubstituted propyl phosphine, asubstituted or unsubstituted butyl phosphine, a substituted orunsubstituted pentyl phosphine, or a substituted or unsubstitutedoctylphosphine (e.g., trioctylphosphine (TOP)); phosphine oxides such assubstituted or unsubstituted methyl phosphine oxide (e.g., trimethylphosphine oxide, methyldiphenyl phosphineoxide, etc.), a substituted orunsubstituted ethyl phosphine oxide (e.g., triethyl phosphine oxide,ethyldiphenyl phosphineoxide, etc.), a substituted or unsubstitutedpropyl phosphine oxide, a substituted or unsubstituted butyl phosphineoxide, and a substituted or unsubstituted octylphosphine oxide (e.g.,trioctylphosphineoxide (TOPO); diphenyl phosphine, triphenyl phosphinecompound, or oxide compound thereof; phosphonic acid, and the like, butare not limited thereof. The organic ligand compound may be used atalone or as a mixture of two or more.

The quantum dot according to an embodiment may be produced in thefollowing method, which includes:

obtaining a first mixture including a first precursor, a ligandcompound, and a solvent (e.g., organic solvent); adding a secondprecursor, a first halogen element source, and a first semiconductornanocrystal to the first mixture to obtain a second mixture;

heating the second mixture up to a reaction temperature to perform areaction between the first precursor and the second precursor; and

adding a second halogen element source to the second mixture afterinitiating the reaction between the first precursor and the secondprecursor.

The first precursor may include at least two compounds. The secondprecursor may include at least two compounds.

When at least two compounds are used for the first and/or the secondprecursors, each compound may be added to the (optionally heated) firstmixture (at the same or different temperature) simultaneously or with apredetermined interval. The first precursor may be mixed with thesame/different ligands and/or the solvents (e.g., an organic solvent) inlight of the shell composition of the final quantum dot to prepare afirst mixture, which is then additionally added. The second precursormay be mixed with the same/different ligands and/or solvents (e.g., anorganic solvent) in view of the shell composition of the final quantumdot and then additionally added to the first mixture at least one time(e.g., twice, three times, four times, five times, or more).

The first precursor may include a Group II metal excluding cadmium, aGroup III metal, a Group IV metal, or a combination thereof. The firstprecursor may be a metal powder, an alkylated metal compound, a metalalkoxide, a metal carboxylate, a metal nitrate, a metal perchlorate, ametal sulfate, a metal acetylacetonate, a metal halide, a metal cyanide,a metal hydroxide, a metal oxide, or a metal peroxide.

Examples of the first precursor may be dimethyl zinc, diethyl zinc, zincacetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinc chloride,zinc fluoride, zinc carbonate, zinc cyanide, zinc nitrate, zinc oxide,zinc peroxide, zinc perchlorate, zinc sulfate, mercury acetate, mercuryiodide, mercury bromide, mercury chloride, mercury fluoride, mercurycyanide, mercury nitrate, mercury oxide, mercury perchlorate, mercurysulfate, lead acetate, lead bromide, lead chloride, lead fluoride, leadoxide, lead perchlorate, lead nitrate, lead sulfate, lead carbonate, tinacetate, tin bisacetylacetonate, tin bromide, tin chloride, tinfluoride, tin oxide, tin sulfate, germanium tetrachloride, germaniumoxide, germanium ethoxide, trimethylgallium, triethylgallium, galliumacetylacetonate, gallium chloride, gallium fluoride, gallium oxide,gallium nitrate, gallium sulfate, trimethylindium, indium acetate,indium hydroxide, indium chloride, indium oxide, indium nitrate, indiumsulfate, thallium acetate, thallium acetylacetonate, thallium chloride,thallium oxide, thallium ethoxide, thallium nitrate, thallium sulfate,thallium carbonate, but are not limited thereto. The first precursor maybe used alone or as a mixture of at least two compounds depending on thefinal composition of the nanocrystal sought to prepare.

The ligand compound (i.e., the organic ligand) is the same as describedabove.

The solvent may be selected from a C6 to C22 primary amine such ashexadecylamine; a C6 to C22 secondary amine such as dioctylamine; a C6to C40 tertiary amine such as trioctylamine; a nitrogen-containingheterocyclic compound such as pyridine; a C6 to C40 aliphatichydrocarbon (e.g., alkane, alkene, alkyne, etc.) such as hexadecane,octadecane, octadecene, and squalane; a C6 to C30 aromatic hydrocarbonsuch as phenyl dodecane, phenyl tetradecane, and phenyl hexadecane; aphosphine substituted with a C6 to C22 alkyl group such astrioctylphosphine, a phosphine oxide substituted with a C6 to C22 alkylgroup such as trioctylphosphine oxide; a C12 to C22 aromatic ether suchas phenyl ether and benzyl ether; and a combination thereof. The solventmay be appropriately selected according to types of the first/secondprecursors, the first/second halogen source, and the organic ligand.

In the first mixture, the amounts of the first precursor, the ligandcompound, and the solvent may be appropriately selected as desired(e.g., in light of a desirable thickness of the shell, types of theprecursors, and the like), and they are not particularly limited. Forexample, a mole ratio between the first precursor and the ligand (firstprecursor: ligand) may be about 1:4 to about 1:0.5, for example, about1:3.5 to about 1:1, or about 1:3 to about 1:1.5, but is not limitedthereto.

The first mixture may optionally be heated. The optional step of heatingthe first mixture may include heating the first mixture under vacuum orunder the inert gas atmosphere at a temperature of greater than or equalto about 40° C., for example, greater than or equal to about 50° C.,greater than or equal to about 60° C., greater than or equal to about70° C., greater than or equal to about 80° C., greater than or equal toabout 90° C., greater than or equal to about 100° C., or greater than orequal to about 110° C. In addition, the method may include heating thefirst mixture under the nitrogen atmosphere at a temperature of greaterthan or equal to about 100° C., for example, at a temperature of greaterthan or equal to about 150° C., or at a temperature of greater than orequal to about 170° C.

A first semiconductor nanocrystal, a second precursor, and a firsthalogen source are simultaneously or sequentially (in any order) addedto the (optionally heated) first mixture to provide a second mixture.

In the second mixture, the amounts of the second precursor, the firsthalogen source and the first semiconductor nanocrystal may beappropriately selected considering a desired composition of the quantumdot, a thickness of the shell, and the like.

Details of the first semiconductor nanocrystal are the same as describedabove.

The second precursor may be appropriately selected according to thetypes of the crystalline/amorphous materials of the shell, and is notparticularly limited thereto. In an embodiment, the second precursor mayinclude a Group V element, a compound including a Group V element, aGroup IV element, or a compound including a Group IV element, or acombination thereof. Examples of the second precursor may be sulfur,selenium, or selenide, tellurium or telluride, phosphorus, arsenic orarsenide, nitrogen or a nitrogen-containing compound, hexane thiol,octane thiol, decane thiol, dodecane thiol, hexadecane thiol, mercaptopropyl silane, sulfur-trioctylphosphine (S-TOP),sulfur-tributylphosphine (S-TBP), sulfur-triphenylphosphine (S-TPP),sulfur-trioctylamine (S-TOA), bis(trimethylsilyl) sulfide, sulfideammonium, sulfide sodium, selenium-trioctylphosphine (Se-TOP),selenium-tributylphosphine (Se-TBP), selenium-triphenylphosphine(Se-TPP), tellurium-tributylphosphine (Te-TBP),tellurium-triphenylphosphine (Te-TPP), tris(trimethylsilyl) phosphine,tris(dimethylamino) phosphine, triethylphosphine, tributylphosphine,trioctylphosphine, triphenylphosphine, tricyclohexylphosphine, arsenicoxide, arsenic chloride, arsenic sulfate, arsenic bromide, arseniciodide, nitric oxide, nitric acid, and ammonium nitrate, but are notlimited thereto. The second precursor may be used alone or in acombination of at least two compounds depending on the final compositionof the nanocrystal sought to be prepared.

The first halogen source may include HF, NH₄F, LiF, NaF, KF, BeF₂, MgF₂,CaF₂, SrF₂, CuF, CuF₂, AgF, AuF, AuF₃, ZnF₂, HgF₂, AlF₃, GaF₃, InF₃,SnF₂, PbF₂, BF₃, HBF₄, a BF₄ ⁻-containing salt such as alkylammoniumtetrafluoroborate, a PF₆ ⁻-containing salt, B(Ar)₃ (wherein, Ar is anaromatic C6 to C20 hydrocarbon group where at least one hydrogen isreplaced by fluorine) such as B(C₆F₅)₃, ionic liquid, or a combinationthereof.

The first halogen source may be added in an amount of about 0.001 mol %to about 500 mol %, for example, greater than or equal to about 0.01 mol%, greater than or equal to about 0.1 mol %, or about 1 mol % to about300 mol %, or about 2 mol % to about 200 mol % to the first mixture,based on the number of moles of the first precursor.

The first halogen source may be added as a solution where the firsthalogen source is dissolved in an intermediate solvent, and theintermediate solvent may be water, acetone, C3 to C12 ketones such asmethylethylketone, primary amines, secondary amines, tertiary amines(e.g. trioctylamine), nitrogen-containing heterocyclic compounds such aspyridine, olefin, aliphatic hydrocarbons, aromatic hydrocarbonssubstituted with a C1 to C20 alkyl group, phosphines substituted withalkyl group, phosphine oxides substituted with alkyl group, aromaticethers, or a combination thereof. In the solution, a molarity of thefluorine source may be greater than or equal to about 0.001 moles perliter (mol/L).

The second mixture is heated at a reaction temperature to perform areaction between the first precursor and the second precursor, and ashell is formed on the first semiconductor nanocrystal. The reactiontemperature is not particularly limited, and may be selectedappropriately based on the first precursor, the second precursor, thehalogen source, and the solvent/organic ligand. For example, thereaction temperature may be greater than or equal to about 100° C., forexample greater than or equal to about 120° C., greater than or equal toabout 150° C., greater than or equal to about 170° C., greater than orequal to about 200° C., greater than or equal to about 210° C., greaterthan or equal to about 220° C., greater than or equal to about 230° C.,greater than or equal to about 240° C., greater than or equal to about250° C., or greater than or equal to about 260° C. For example, thereaction temperature may be less than or equal to about 350° C., forexample less than or equal to about 340° C., less than or equal to about330° C., less than or equal to about 320° C., or less than or equal toabout 310° C. For example, the reaction temperature may be about 220° C.to about 320° C. or about 280° C. to about 320° C.

The reaction time is not particularly limited, and may be appropriatelyselected. For example, the reaction may be performed for greater than orequal to about 5 minutes, greater than or equal to about 10 minutes, orgreater than or equal to about 15 minutes, but is not limited thereto.When the precursor mixture is added stage by stage, a reaction in eachstage may be performed for a predetermined time (e.g., greater than orequal to about 5 minutes, greater than or equal to about 10 minutes, orgreater than or equal to about 15 minutes). The reaction involving thehalogen source may proceed rapidly, and may be performed for about 1second or longer, for example, for about 10 seconds or longer, about 30seconds or longer, about 1 minute or longer, about 5 minutes or longer,about 10 minutes or longer, or about 15 minutes or more, but it is notlimited thereto. The reaction may be performed under an inert gasatmosphere, air, or vacuum, but is not limited thereto.

In the reaction between the first precursor and the second precursor,the crystal or amorphous material is formed and deposited on the surfaceof the first semiconductor nanocrystal (particle) to provide the quantumdots with a core-shell structure. When the first nanocrystal has acore-shell structure, the final nanocrystal particles may have acore-multi shell structure and include a first halogen atom on the outerlayer of shell.

The crystalline or amorphous material formed by the reaction between thefirst precursor and the second precursor is the same as described above.

After the initiation of the reaction between the first precursor and thesecond precursor, in other words, after the formation of one or at leastone of a plurality of monolayers (i.e., greater than or equal to onemonolayer) of the crystalline or amorphous material, the second halogensource is added to the second mixture. The method may include furtheradding the second precursor (or a mixture of the second precursor and anorganic solvent and/or a ligand) to the second reaction mixture(hereinafter, the additional addition of the second precursor), afterthe initiation of the reaction between the first precursor and thesecond precursor. The second halogen source may be added prior to orafter the additional addition of the second precursor.

The second halogen source may include chlorine, bromine, iodine, or acombination thereof. The second halogen source may be a metal halide, anorganic halide, or a combination thereof. The metal halide may includethe same metal as the metal of the first precursor. Examples of thesecond halogen source may be HCl, NH₄Cl, HBr, NH₄Br, LiCl, NaCl, KCl,BeCl₂, MgCl₂, CaCl₂, SrCl₂, CuCl, AgCl, AuCl, ZnCl₂, HgCl₂, AlCl₃,GaCl₃, InCl₃, SnCl₂, PbCl₂, LiBr, NaBr, KBr, BeBr₂, MgBr₂, CaBr₂, SrBr₂,CuBr, AgBr, AuBr, ZnBr₂, CdBr₂, HgBr₂, AlBr₃, GaBr₃, InBr₃, SnBr₂,PbBr₂, LiI, NaI, KI, BeI₂, MgI₂, CaI₂, SrI₂, CuI, AgI, AuI, ZnI₂, CdI₂,HgI₂, AlI₃, GaI₃, InI₃, SnI₂, PbI₂, a C1 to C20 aliphatic hydrocarbonchloride (e.g., CCl₄, CHCl₃, dichloroethane, tetrachloroethane,tetrachloroethylene, or hexachloroethane), a C1 to C20 aliphatichydrocarbon bromide (e.g., dibromoethane, tetrabromoethane, orhexabromoethane), a C1 to C20 aliphatic hydrocarbon iodide (e.g.,diiodoethane or tetraiodoethane) or a combination thereof, but is notlimited thereto.

The amount of the second halogen source used may be selectedappropriately. For example, the second halogen source may be added in anamount of about 0.001 mol % to about 500 mol %, for example, greaterthan or equal to about 0.01 mol %, greater than or equal to about 0.1mol %, or about 1 mol % to about 300 mol % or about 2 mol % to about 200mol % based on the moles of the first metal precursor.

The aforementioned method of synthesizing the quantum dot may furtherinclude adding reaction products of the first/second precursors to anonsolvent and separating nanocrystals coordinated with the ligandcompound. The nonsolvent may be a polar solvent that is miscible withthe solvent used in the reaction but cannot disperse nanocrystals. Thenonsolvent may be determined according to the solvent used in thereaction, and may be, for example, acetone, ethanol, butanol,isopropanol, ethanediol, water, tetrahydrofuran (THF), dimethylsulfoxide(DMSO), diethylether, formaldehyde, acetaldehyde, a solvent having asimilar solubility parameter to the foregoing solvents, or a combinationthereof. The separating may be performed using centrifugation,precipitation, chromatography, or distillation. The separatednanocrystal may be added to a rinsing solvent as needed. The rinsingsolvent is not particularly limited, and may be a solvent having asimilar solubility parameter to the ligand, and examples thereof may behexane, heptane, octane, chloroform, toluene, benzene, and the like.

In another embodiment, a quantum dot polymer composite includes apolymer matrix; and

the quantum dot dispersed in the polymer matrix.

The polymer matrix may include a thiolene polymer, a (meth)acrylatepolymer, a urethane polymer, an epoxy polymer, a vinyl polymer, asilicone polymer, or a combination thereof. The thiolene polymer isdisclosed in US-2015-0218444-A1, which is incorporated herein byreference in its entirety. The (meth)acrylate polymer, the urethanepolymer, the epoxy polymer, the vinyl polymer, and the silicone polymermay be synthesized by a known method, or a monomer or polymer thereofmay be commercially available.

In the polymer matrix, an amount of the quantum dot may be appropriatelyselected and is not particularly limited. For example, in the polymermatrix, a content of the quantum dot may be greater than or equal toabout 0.1 wt % and less than or equal to about 30 wt % based on thetotal weight of the composite, but is not limited thereto.

The quantum dot polymer composite may be prepared by mixing thedispersion including the quantum dots with a solution including thepolymer and removing the solvent. Alternatively, it may be prepared bydispersing the quantum dots in the monomer mixture for forming thepolymer and polymerizing the obtained final mixture. The quantumdot-polymer composite may be a quantum dot sheet (QD sheet).

Another embodiment provides an electronic device including the quantumdots. The details of the semiconductor nanocrystal particle are same asin above. The device includes a light emitting diode (LED), and organiclight emitting diode (OLED), various types of displays (e.g., liquidcrystal display (LCD)), a sensor, a solar cell, or an imaging sensor,but is not limited thereto. FIG. 3 is a schematic view showing astacking structure of a liquid crystal display (LCD) including a quantumdot sheet among the devices. The general structure of liquid crystaldisplay (LCD) is well known, and FIG. 3 schematically shows thestructure.

Referring to FIG. 3, the liquid crystal display may have a structure inwhich a reflector, a light guide panel (LGP) and a blue LED light source(Blue-LED), a quantum dot-polymer composite sheet (QD sheet), thevarious types of optical films, for example, a prism, a doublebrightness enhance film (DBEF) or the like are stacked, and a liquidcrystal panel is disposed thereon.

Hereinafter, the exemplary embodiments are illustrated in more detailwith reference to specific examples. However, they are exemplaryembodiments, and the present disclosure is not limited thereto.

EXAMPLES

Analysis Method

Photoluminescence Analysis of Quantum Dots (Solution State)

It obtains a photoluminescence (PL) spectrum of quantum dots prepared ata radiation wavelength of 458 nanometers (nm) (in a case of red QD, at532 nm) using a Hitachi F-7000 spectrometer.

Photoluminescence Analysis of Quantum Dot (Film)

It obtains a photoluminescence (PL) spectrum of a quantum dot-polymercomposite prepared at a radiation wavelength of 458 nm (in the case ofred QD, at 532 nm) using a PSI DARSA-5200 spectrometer.

UV Spectroscopic Analysis

UV spectroscopic analysis is performed using a Hitachi U-3310spectrometer to provide a UV-Visible absorption spectrum.

XPS Analysis

Using a Quantum 2000 device manufactured by Physical Electronics, a XPSatomic analysis is performed under the condition of accelerationvoltage: 0.5-15 keV, 300 W, minimum analysis region: 200×200 μm².

Thermal Quenching Analysis

A quantum dot polymer composite film is performed with a thermalquenching analysis within a temperature range of 25° C. to 150° C. usinga spectrometer (manufacturer: PSI, model name: DARSA-5200).

Reference Example 1 Production of InP Core

0.2 mmol of indium acetate, 0.125 mmol of zinc acetate, 0.6 mmol ofpalmitic acid, 10 mL of 1-octadecene are placed into a reactor andheated at 120° C. under vacuum. The atmosphere in the reactor issubstituted with nitrogen after one hour. After heating at 280° C., amixed solution of 0.15 mmol of tris(trimethylsilyl)phosphine (TMS3P) and1 mL of trioctylphosphine is rapidly added thereto and reacted for 20minutes. The reaction solution is rapidly cooled to room temperature andadded with acetone and centrifuged to provide a precipitate, and theprecipitate is dispersed in toluene. An UV Spectroscopic Analysis ismade and it is confirmed in a UV spectrum UV first absorption maximumwavelength is 440 nm, so the core diameter is 2.16 nm.

Example 1

1.8 mmol (0.336 gram (g)) of zinc acetate, 3.6 mmol (1.134 g) of oleicacid, and 10 mL of trioctylamine are placed into a flask and vacuumed at120° C. for 10 minutes. Nitrogen (N₂) is substituted in the flask andheated at 180° C.

InP core obtained from Reference Example 1 is placed therein within 10seconds, and subsequently slowly added with 0.04 mmol of Se/TOP andheated at 280° C. Then 0.01 mmol of S/TOP is added thereto (firstaddition) and heated at 320° C. and reacted for 10 minutes.

Subsequently, a mixed solution of 0.02 mmol of Se/TOP and 0.04 mmol ofS/TOP is slowly added (second addition) thereto and reacted again at320° C. for 20 minutes. Then, as a first halogen source, a mixedsolution of 0.36 mmol of HF (aqueous solution 3 μL)/25 μL of acetone(intermediate solvent) is added, and right after then, a mixed solutionof Se/TOP 0.01 mmol+S/TOP 0.05 mmol is slowly added (third addition) andreacted again at 320° C. for 20 minutes. Then, as a second halogensource, a mixed solution of 0.18 mmol of ZnCl₂/50 μL of acetone(intermediate solvent) is added and right after then, a mixed solutionof Se/TOP 0.005 mmol+S/TOP 0.1 mmol is added (fourth addition) andreacted at 320° C. for 20 minutes. 0.5 mmol of S/TOP solution is added(fifth addition) and reacted at 280° C. for one hour.

After the reaction in each addition step, a small amount of sample istaken from the reaction solution and a quantitative analysis of theshell component was evaluated using inductive coupling plasma analysisto find a shell thickness. The results are shown in the following Table1:

TABLE 1 Shell thickness ZnSeS ICP ZnSeS (the number of Samples S/InZn/In Se/In (nm) monolayers) 1 step addition 0.462 5.129 3.602 0.718 1-22 step addition 1.254 7.582 4.507 0.888 3 3 step addition 2.760 10.0005.620 1.102 3 4 step addition 6.382 15.000 6.353 1.376 4 5 step addition13.435 22.087 6.217 1.707 5

It is confirmed that the shell has grown to have a thickness of about 1to 2 (monolayers) ML after the first adding reaction.

After completing all reactions, the reactor is cooled, and the obtainednanocrystal is centrifuged in ethanol and dispersed in toluene. Theobtained nanocrystal (QD) has a UV first absorption maximum wavelengthof about 500-515 nm, a PL emission peak of about 520-545 nm, FWHM ofabout 38-44 nm.

Comparative Example 1 Halogen-Free InP/ZnSeS (Core/Shell) Quantum Dot

InP/ZnSeS (core/shell) quantum dot is synthesized in accordance with thesame procedure as in Example 1, except that the first halogen source andthe second halogen source are not used. The obtained nanocrystal (QD)has a PL emission peak of 531 nm and FWHM of 43 nm.

Comparative Example 2 InP/ZnSeS (Core/Shell) Quantum Dot with Fluorineand No Chlorine

InP/ZnSeS (core/shell) quantum dot including fluorine in a shell issynthesized in accordance with the same procedure as in Example 1,except that the second halogen source is not used. The obtainednanocrystal (QD) has a PL emission peak of 536 nm and FWHM of 40 nm.

Example 2

Quantum dot is synthesized in accordance with the same procedure as inExample 1, except that trichloromethane (CHCl₃) is used instead of theZnCl₂ solution.

The obtained quantum dot (QD) has a PL emission peak of 536 nm and aFWHM of 40 nm.

Example 3

Quantum dot is synthesized in accordance with the same procedure as inExample 1, except that 1,2-dichloroethane(DCE: C₂H₄Cl₂) is used insteadof the ZnCl₂ solution.

The obtained quantum dot (QD) has a PL emission peak of 531 nm and aFWHM of 40 nm.

Example 4

Quantum dot is synthesized in accordance with the same procedure as inExample 1, except that hexachloroethane (HCE: C₂Cl₆) is used instead ofthe ZnCl₂ solution.

The obtained quantum dot (QD) has a PL emission peak of 532 nm and aFWHM of 40 nm.

Example 5

Quantum dot is synthesized in accordance with the same procedure as inExample 1, except that 1,1,2,2-tetrachloroethylene (TCE: C₂Cl₄) is usedinstead of the ZnCl₂ solution.

The obtained quantum dot (QD) has a PL emission peak of 532 nm and aFWHM of 40 nm.

Example 6

Quantum dot is synthesized in accordance with the same procedure as inExample 1, except that instead of the ZnCl₂ solution, a mixed solutionof the solution including 0.9 mmol of ZnCl₂ and 250 μL of acetone (asintermediate solvent) is used. The obtained quantum dot (QD) has a PLemission peak of 531 nm and a FWHM of 42 nm.

Experimental Example 1-1 Production of Quantum Dot-Polymer Composite

30 wt % of lauryl methacrylate, 36 wt % of tricyclodecane dimethanoldiacrylate, 4 wt % of trimethylol propane triacrylate, 20 wt % of epoxydiacrylate oligomer (manufacturer: Sartomer), 1 wt % of1-hydroxy-cyclohexyl-phenyl-ketone, and 1 wt % of2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide are mixed to provide amixture of monomer and oligomer. The mixture is defoamed under vacuum.

In Example 1 to 6, Comparative Example 1 and Comparative Example 2, eachof the synthesized quantum dots is centrifuged. The toluene dispersionof the obtained quantum dots [concentration: (absorption at 449nm)×(volume of QD solution (mL))=3.75] is mixed with the excess amountof ethanol again and centrifuged. The separated quantum dots aredispersed in 0.15 g (10 wt % of the entire composition except theinitiator) of laurylmethacrylate and then added into the preparedmonomer (oligomer) mixture (1.35 g) and stirred (vortexing) to provide asemiconductor nanocrystal composition.

About 1 g of semiconductor nanocrystal composition thus obtained isdrop-casted on a PET film sputtered with SiOx as a barrier film on onesurface (manufactured from I-component, hereinafter referred to barrierfilm). Another barrier film is covered on the composition and cured byUV light for 10 seconds (light intensity: 100 mW/cm²) to provide aquantum dot-polymer composite sheet.

Experimental Example 1-2 Photoluminescence Characteristics

Each of quantum dot polymer composite sheets obtained from ExperimentalExample 1-1 is measured for a photoconversion efficiency (CE) accordingto the following method:

The quantum dot-polymer composite sheet is inserted between the lightguide panel and the optical sheet of a 60 inch TV mounted with a blueLED having a peak wavelength of 449 nm.

From the spectrum obtained by a spectroradiometer (Konica Minolta,CS-2000) located about 45 cm in front of the operating TV, aphotoconversion efficiency is calculated by the following formula:Photoconversion Efficiency=(green or red light emission peakarea)/(light emission area of blue LED chip before emitting green or redlight−blue light emission area when emitting the green or redlight)×100.

A ratio (%) of the relative photoconversion efficiency of ComparativeExample 2 and each Example with respect to the photoconversionefficiency (100%) of a sheet including quantum dots according toComparative Example 1 is shown in the following Table 2:

TABLE 2 Relative Halogen(s) in photoconversion shell efficiency of filmComparative Example 1 — 100% Comparative Example 2 F 102.9%   Example 1F, Cl 106.1%   Example 2 F, Cl 106% Example 3 F, Cl 106% Example 4 F, Cl104.2%   Example 5 F, Cl 104%

From the results of Table 2, it is confirmed that the photoconversionefficiencies of films including QD according to Comparative Example 2and Examples 1 to 5 are greater than the photoconversion efficiency offilm including quantum dots according to Comparative Example 1.

Experimental Example 1-3 Evaluation of Thermal Quenching Phenomenon

For each quantum dot polymer composite sheet obtained from ExperimentalExample 1-1, a thermal quenching phenomenon is evaluated as follows:

The quantum dot polymer composite film is inserted into a PSI DARSA-5200spectrometer. The temperature of the holder is controlled at 25° C. andirradiated with blue light and measured for a photoluminescenceintensity (that is directly related to the solid state photoluminescentquantum efficiency(QE) of the quantum dots dispsersed in the sheet), andthen the temperature is increased to 50° C. When the temperature reaches50° C., the film is irradiated with blue light again and measured for aphotoluminescence intensity. The same measurement is then performed at75° C., 100° C., 125° C., and 150° C. The amount of thermal quenching isdetermined as follows:

The relative photoluminescence intensity (%) at each temperature to thephotoluminescence intensity (100%) at 25° C. is obtained.

The results are shown in Table 3 and FIG. 2.

TABLE 3 QE percentage (%) at each temperature when QE at 25° C. is 100%Temperature Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 (° C.) Ex. 1Ex. 2 ZnCl₂ CHCl₃ DCE HCE TCE ZnCl₂ 25 100 100.0 100 100 100.0 100.0100.0 100.0 50 98.6 101.1 101.3 100.7 100.8 103.1 100.8 75 95.4 100.199.7 101.6 101.2 100.4 100 79.5 88.8 98.7 97.2 95.2 97.3 98.2 97.6 12580.5 95.0 88.4 93.3 91.8 94.0 150 64.6 70.7 89.4 84.2 80.4 86.0 83.289.0

From the results of Table 3 and FIG. 2, it is confirmed that the sheetsincluding quantum dots according to Example 1 may have a quantumefficiency at greater than or equal to 95° C. of greater than or equalto about 90% (for example, the quantum efficiency at 100° C. of 98.7%,and the quantum efficiency at 150° C. of 89.4%) with respect to thequantum efficiency at 25° C. The sheets including quantum dots accordingto Comparative Examples have a photoconversion efficiency at 100° C. anda photoconversion efficiency at 150° C. that are less than those of thesheets including quantum dots according to Examples.

Experimental Example 1-4 XPS Analysis

Quantum dots obtained from Example 1 and Quantum dots obtained fromComparative Example 2 are evaluated by an XPS analysis, and the resultsare shown in the following Table 4:

TABLE 4 Atomic ratio of each element (S, Cl, Zn, or Se) with respect toindium S (2p) Cl (2p) Zn (2p3) Se (3d) Comparative Example 2 6.79 —13.60 6.45 Example 1 8.92 0.71 16.37 6.74

From the results of Table 4, it is confirmed that Cl is present in thequantum dots according to Example 1.

Example 7

Quantum dots are synthesized in accordance with the same procedure as inExample 1, except that a LiCl organic solution is used instead of theZnCl₂ solution.

The obtained QD has a PL emission peak of 538 nm and a FWHM of 39 nm.

Example 8

Quantum dots are synthesized in accordance with the same procedure as inExample 1, except that a LiBr organic solution is used instead of theZnCl₂.

The obtained QD has a PL emission peak of 537 nm and a FWHM of 40 nm.

Comparative Example 3

Quantum dots are synthesized in accordance with the same procedure as inExample 1, except HF (i.e., first halogen source) is not used, and aZnCl₂ organic solution is used.

The obtained QD has a PL emission peak of 529 nm and a FWHM of 42 nm.

Comparative Example 4

Quantum dots are synthesized in accordance with the same procedure as inExample 1, except HF (i.e., first halogen source) is not used, and aZnBr₂ organic solution is used instead of the ZnCl₂ solution.

The obtained QD has a PL emission peak of 531 nm and a FWHM of 42 nm.

Comparative Example 5

Quantum dots are synthesized in accordance with the same procedure as inExample 1, except HF (i.e., first halogen source) is not used, and boththe ZnCl₂ solution and the ZnBr₂ solution are used.

The obtained QD has a PL emission peak of 529 nm and a FWHM of 44 nm.

Experimental Example 2-1

A quantum dot-polymer composite sheet is prepared in accordance with thesame procedure as in Experimental Example 1-1, except that each quantumdot synthesized from Example 7, Example 8, Comparative Example 3,Comparative Example 4, and Comparative Example 5 is used.

Experimental Example 2-2

Each of the quantum dot polymer composite sheets obtained fromExperimental Example 2-1 is measured for a photoconversion efficiency(CE) in accordance with the same procedure as in Experimental Example1-2. The results are shown in Table 5.

TABLE 5 Relative photoconversion Halogen in shell efficiency of filmComparative Example 1 —   100% Example 7 F, Cl 105.2% Example 8 F, Br105.4% Comparative Example 3 Cl 100.7% Comparative Example 4 Br 100.7%Comparative Example 5 Cl, Br  99.2%

From Table 5, it is confirmed that the quantum dot-polymer compositeincluding quantum dots including fluorine and chlorine, fluorine andbromine in the shell have improved photoconversion efficiency comparedto the quantum dots according to Comparative Examples.

Example 9

Quantum dots (Examples 9-1, 9-2, 9-3, 9-4 and 9-5) are synthesized inaccordance with the same procedure as in Example 1, except that theadding time of ZnCl₂ solution is changed as in the following Table 6. PLemission peak, and FWHM of the obtained quantum dots are shown in thefollowing Table 6.

A quantum dot-polymer composite sheet is prepared in accordance with thesame procedure as in Experimental Example 1-1, except that quantum dotsof Examples 9-1, 9-2, 9-3, 9-4 and 9-5 are used, respectively. Each ofthe obtained quantum dot polymer composite sheets is measured for arelative photoconversion efficiency in accordance with the sameprocedure as in Experimental Example 1-2. The results are shown in Table6.

Comparative Example 6

Quantum dots are synthesized in accordance with the same procedure as inExample 1, except that the ZnCl₂ solution is simultaneously added on thefirst addition (i.e., simultaneously added with the first semiconductornanocrystal).

The quantum dot-polymer composite sheet is prepared in accordance withthe same procedure as in Experimental Example 1-1, except that theobtained quantum dots are used. Each of the obtained quantum dot polymercomposite sheets is measured for a relative photoconversion efficiencyin accordance with the same procedure as in Experimental Example 1-2.The results are shown in Table 6.

TABLE 6 Photoluminescence Relative properties photoconversion Additiontime of quantum dot efficiency of film (CE) ZnCl₂ (mole ratio with @458FWHM   100% respect to amount of (nm) (nm) first precursor = 1/10)Example 9-1 3 step addition 528 42 105.6% (reaction temperature = 320°C.) Example 9-2 4 step addition 531 41 104.8% (reaction temperature =200° C.) Example 9-2 4 step addition 536 39 105.6% (reaction temperature= 320° C.) Example 9-2 Addition in 10 min. 530 41 105.0% after 4 stepaddition Example 9-2 Addition in 20 min. 531 40 105.2% after 4 stepaddition Comparative Example 6 1 step addition (i.e., 533 nm 42 nm   80%addition of first semiconductor nanocrystal) with second halogen source(Cl)

From the results shown in Table 6, it is confirmed that it may improvethe photoluminescence properties of quantum dots and the photoconversionefficiency of the film including the same when adding the second halogensource after initiating the reaction of the first precursor and thesecond precursor. When the halogen source is added together with a core(i.e., first semiconductor nanocrystal), the halogen may have reactedbefore forming the shell to a predetermined thickness (e.g., greaterthan or equal to 1 ML), and it may be confirmed that enhancing effectsare not observed.

While this disclosure has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A quantum dot having a core-shell structure, thecore-shell structure comprising: a core comprising a first semiconductornanocrystal; and a shell disposed on the core, the shell comprising acrystalline or amorphous material and at least two different halogens,wherein the quantum dot does not include cadmium, wherein a solid statephotoluminescence quantum efficiency of the quantum dot, when measuredat 90° C. or greater, is greater than or equal to about 95% of a solidstate photoluminescence quantum efficiency of the quantum dot whenmeasured at 25° C., and wherein the at least two different halogenscomprise fluorine and at least one of chlorine and bromine.
 2. Thequantum dot of claim 1, wherein the at least two different halogensconsist of either fluorine and chlorine or fluorine and bromine.
 3. Thequantum dot of claim 1 wherein the first semiconductor nanocrystalcomprises indium and phosphorous and the crystalline or amorphousmaterial of the shell comprises zinc and at least one of sulfur andselenium.
 4. The quantum dot of claim 1, wherein a solid statephotoluminescence quantum efficiency of the quantum dot when measured at100° C. is greater than or equal to about 95% of the solid statephotoluminescence quantum efficiency of the quantum dot when measured at25° C.
 5. The quantum dot of claim 1, wherein a solid statephotoluminescence quantum efficiency of the quantum dot when measured ata 150° C. is greater than or equal to about 80% of the solid statephotoluminescence quantum efficiency of the quantum dot when measured at25° C.
 6. The quantum dot of claim 1, wherein each halogen is present inor on the shell in a doped form or in a form of a metal halide.
 7. Thequantum dot of claim 1, wherein the shell has a thickness of at leastone monolayer of the material of the shell, and at least one of thehalogens is present at or outside the thickness of the one monolayer. 8.The quantum dot of claim 1, wherein a total amount of the two or morehalogens is greater than or equal to about 30 atomic percent, withrespect to a total amount of a metal atom included in the core.
 9. Thequantum dot of claim 1, wherein the first semiconductor nanocrystalcomprises at least one first metal selected from a group consisting of aGroup II metal excluding cadmium, a Group III metal, a Group IV metal,and a combination thereof, and wherein the crystalline or amorphousmaterial of the shell comprises at least one second metal that isdifferent form the first metal and is selected from the group consistingof a Group I metal, a Group II metal excluding cadmium, a Group IIImetal, a Group IV metal, and a combination thereof.
 10. The quantum dotof claim 9, wherein, the Group II-VI compound comprises ZnS, ZnSe, ZnTe,ZnO, HgS, HgSe, HgTe, MgSe, MgS, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe,HgSTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, HgZnTeS, HgZnSeS, HgZnSeTe,or a combination thereof, the Group III-V compound comprises GaN, GaP,GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, GaNP, GaNAs,GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs,InNSb, InPAs, InPSb, GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP,GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs,InAlPSb, or a combination thereof, the Group IV-VI compound comprisesSnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe,PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, SnPbSTe, or acombination thereof, the Group I-III-VI compound comprises CuInSe₂,CuInS₂, CuInGaSe, CuInGaS, or a combination thereof, the Group II-III-VIcompound comprises ZnGaS, ZnAlS, ZnInS, ZnGaSe, ZnAlSe, ZnInSe, ZnGaTe,ZnAlTe, ZnInTe, ZnGaO, ZnAlO, ZnInO, HgGaS, HgAlS, HgInS, HgGaSe,HgAlSe, HgInSe, HgGaTe, HgAlTe, HgInTe, MgGaS, MgAlS, MgInS, MgGaSe,MgAlSe, MgInSe, or a combination thereof, the Group I-II-IV-VI compoundcomprises CuZnSnSe, CuZnSnS, or a combination thereof, the Group IVelement compound comprises Si, Ge, SiC, SiGe, or a combination thereof,the metal-containing halogen compound comprises LiF, NaF, KF, BeF₂,MgF₂, CaF₂, SrF₂, CuF, AgF, AuF, ZnF₂, HgF₂, AlF₃, GaF₃, InF₃, SnF₂,PbF₂, LiCl, NaCl, KCl, BeCl₂, MgCl₂, CaCl₂, SrCl₂, CuCl, AgCl, AuCl,ZnCl₂, HgCl₂, AlCl₃, GaCl₃, InCl₃, SnCl₂, PbCl₂, LiBr, NaBr, KBr, BeBr₂,MgBr₂, CaBr₂, SrBr₂, CuBr, AgBr, AuBr, ZnBr₂, HgBr₂, AlBr₃, GaBr₃,InBr₃, SnBr₂, PbBr₂, LiI, NaI, KI, BeI₂, MgI₂, CaI₂, SrI₂, CuI, AgI,AuI, ZnI₂, HgI₂, AlI₃, GaI₃, InI₃, SnI₂, PbI₂, or a combination thereof,and the metal oxide comprises In₂O₃, PbO, HgO, MgO, Ga₂O₃, Al₂O₃, ZnO,SiO₂, zinc oxysulfide, zinc oxyselenide, zinc oxysulfide selenide,indiumphosphide oxide, indiumphosphide oxysulfide, or a combinationthereof.
 11. The quantum dot of claim 1, wherein the first semiconductornanocrystal comprises a Group II-VI compound excluding acadmium-containing compound, a Group III-V compound, a Group IV-VIcompound, a Group IV element or compound, a Group II-III-VI compound, aGroup I-III-VI compound, a Group I-II-IV-VI compound, or a combinationthereof, and wherein the material of the shell comprises a Group II-VIcompound excluding a cadmium-containing compound, a Group III-Vcompound, a Group IV-VI compound, a Group IV element or compound, aGroup II-III-VI compound, a Group I-III-VI compound, a Group I-II-IV-VIcompound, a metal-containing halogen compound, a metal oxide, or acombination thereof.
 12. The quantum dot of claim 1, wherein the firstsemiconductor nanocrystal comprises a Group III-V compound, and theshell comprises a Group II-VI compound.
 13. The quantum dot of claim 1,wherein the quantum dot has a quantum yield of greater than or equal toabout 85%.
 14. A quantum dot polymer composite comprising a polymermatrix; and the quantum dot of claim 1 dispersed in the polymer matrix.15. The quantum dot polymer composite of claim 14, wherein the polymermatrix comprises a thiolene polymer, a (meth)acrylate polymer, aurethane polymer, an epoxy polymer, a vinyl polymer, a silicone polymer,or a combination thereof.
 16. An electronic device comprising thequantum dot of claim
 1. 17. A method of producing a quantum dot, themethod comprising: obtaining a first mixture comprising a firstprecursor, a ligand compound, and a solvent; adding a second precursor,a first halogen source, and a first semiconductor nanocrystal to thefirst mixture to obtain a second mixture; heating the second mixture toa reaction temperature effective to perform a reaction between the firstprecursor and the second precursor; and adding a second halogen sourceto the second mixture after initiation of the reaction between the firstprecursor and the second precursor, wherein a core-shell structure ofthe quantum dot comprises a core comprising a first semiconductornanocrystal, and a shell comprising a crystalline or amorphous materialdisposed on the core, wherein the quantum dot does not include cadmium,and wherein the shell comprises at least two different halogens.
 18. Themethod of claim 17, wherein a solid state photoluminescence quantumefficiency of the quantum dot when measured at 90° C. or greater isgreater than or equal to about 95% of a solid state photoluminescencequantum efficiency the quantum dot when measured at 25° C.
 19. Themethod of claim 17, wherein the first precursor comprises a Group IImetal excluding cadmium, a Group III metal, a Group IV metal, or acombination thereof, wherein the metal is a metal powder, an alkylatedmetal compound, a metal alkoxide, a metal carboxylate, a metal nitrate,a metal perchlorate, a metal sulfate, a metal acetylacetonate, a metalhalide, a metal cyanide, a metal hydroxide, a metal oxide, or a metalperoxide, and wherein the second precursor comprises a Group V element,a Group IV element, or a compound including the Group V element, or theGroup IV element.
 20. The method of claim 17, wherein the ligandcompound comprises a compound of the formula RCOOH, RNH₂, R₂NH, R₃N,RSH, R₃PO, R₃P, ROH, RCOOR′, RPO(OH)₂, R₂POOH, wherein each R and R′ areindependently a substituted or unsubstituted C1 to C24 aliphatichydrocarbon group or a substituted or unsubstituted C6 to C20 aromatichydrocarbon group, or a combination thereof.
 21. The method of claim 17,wherein the first halogen source comprises fluorine, and wherein thesecond halogen source comprises chlorine, bromine, iodine, or acombination thereof.
 22. The method of claim 21, wherein the firsthalogen source comprises HF, NH₄F, LiF, NaF, KF, BeF₂, MgF₂, CaF₂, SrF₂,CuF, AgF, AuF, ZnF₂, HgF₂, AlF₃, GaF₃, InF₃, SnF₂, HBF₄, PbF₂, an ionicliquid containing fluorine, or a combination thereof, and the secondhalogen source comprises HCl, NH₄C1, HBr, NH₄Br, LiCl, NaCl, KCl, BeCl₂,MgCl₂, CaCl₂, SrCl₂, CuCl, AgCl, AuCl, ZnCl₂, HgCl₂, AlCl₃, GaCl₃,InCl₃, SnCl₂, PbCl₂, LiBr, NaBr, KBr, BeBr₂, MgBr₂, CaBr₂, SrBr₂, CuBr,AgBr, AuBr, ZnBr₂, HgBr₂, AlBr₃, GaBr₃, InBr₃, SnBr₂, PbBr₂, LiI, NaI,KI, BeI₂, MgI₂, CaI₂, SrI₂, CuI, AgI, AuI, ZnI₂, HgI₂, AlI₃, GaI₃, InI₃,SnI₂, PbI₂, an aliphatic hydrocarbon chloride, an aliphatic hydrocarbonbromide, an aliphatic hydrocarbon iodide, or a combination thereof. 23.The method of claim 17, further comprising adding an additional amountof the second precursor to the second mixture after initiating thereaction between the first precursor and the second precursor.
 24. Themethod of claim 17, wherein an amount of the second halogen source isgreater than an amount of the first halogen source.